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Leak Troughlines

Discussion in 'classic' started by Andrew L Weekes, Jul 31, 2003.

  1. Andrew L Weekes

    Andrew L Weekes Senior Reverse Engineer

    There's been a bit of talk about the Leak tuners in another thread on the Quad FM units.

    Here's a site I found some time ago with some useful information, including a TLII schematic for those interested in the inside.


    I have to get me one of these, it's about time I zapped my fingers with some valves ;)

    Here's a HiFi World article on the Tim deParavicini Stereo decoder


    Here's where the Guru's hang out


    Another stereo decoder


  2. Mr Perceptive

    Mr Perceptive Perceptive Member

  3. hifienthusiast

    hifienthusiast Vintage by heart

    I have a mono troughline, but it is not working very well. GT Audio and Classique Sound in Leicester both offer alignment service for the troughline.

    Has anyone done the alignment and servicing of the troughline themselves?

  4. eguth

    eguth pfm Member

  5. Tony L

    Tony L Administrator

    I recently picked up a unrestored MkI Troughline for peanuts:


    I plan eventually to restore it and put it to work in my upcoming mono system (TL12 Plus and Wharfedale SFB/3), this being its original context.
  6. George J

    George J Herefordshire member


    Brilliant! Mono is fine for music! It may not please those most interested in Hifi effects, but for music it just draws you in. A bit like a black and white film is often easier on the eye than the obvious artificiality of delivery of Technicolor specials!

    ATB from George
    Last edited: Dec 23, 2017
  7. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    I've got one of those MkI's also but have never got round to trying it...

    I have loads of Troughlines if anyone's after one. Sold as seen. Maybe a dozen available.

    They are probably the best British valved hi fi FM tuner, especially for mono, but as usual when the subject comes up I'll say that I regard them as hugely over rated in the context of modern hi fi. The Stereofetic SS unit that replaced it is vastly superior in every way and in fact a very good tuner.

    It is largely a fallacy that you are even getting "valve sound" from a Troughline as nearly all the valves operate at RF. The IF is only changed to audio at the Foster-Seeley detector and then passed through a single valve used as a cathode follower at the output, which won't add much "valve sound". If you take the output from the multiplex socket on the back to feed a stereo decoder then even this is bypassed and there are no valves in the signal path at audio frequencies!

    The best ones are the later "Troughline Stereo" but ironically the first thing you need to do is remove the (solid state) stereo decoder as it's truly shite!! It's so bad that it makes everything sound like "granny's radiogram"! They do have a few modifications on them to improve performance and especially stereo performance. An ECC88 is used as the RF amp to increase sensitivity and give better signal to noise ratio on stereo broadcasts. A few components are changed around this valve and an inductor added. A damping resistor is added across the Foster-Seeley to broaden bandwidth and give better results in a stereo context as well. These mods can all be retro fitted to earlier Troughlines and indeed were by the factory when earlier units were sent back for conversion to stereo versions. I've done a few such conversions myself. I don't offer an alignment service as to do the job properly would cost more than any sane person would want to pay IMHO.
  8. davidsrsb

    davidsrsb pfm Member

    The modern add on stereo decoder is usually an application note MC1310 design, so identical to 90% of solid state tuners out ther
  9. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    And? It's a hell of a lot better than the one used by Leak (Mullard) which is truly dire! Implementation is everything though and for excellent results a high impedance pre amp followed by an active filter should really be used and then the stereo outputs need filtering and buffering. I've used the Hitachi HA11223 with good results in a tuner I designed for Alchemist Products and for the perfectionist there is a discrete stereo decoder design available from John Linsley Hood.
  10. davidsrsb

    davidsrsb pfm Member

    The Hitachi was a decent chip, but like all analog decoder ICs, seems to have vanished. Most ICs are not available from reliable sources.
    Stereo decoding is one of those functions that might be best done in DSP - it would be much easier to compensate for IF group delay errors and and analog multipliers are not as linear as maths
  11. Jim Audiomisc

    Jim Audiomisc pfm Member

    If you want to do a decoder using DSP then you probably might as well go the whole hog and use a Software Defined Radio! 8-] Adding the ADC, DACs, etc, to an old tuner seems a little OTT to me.

    You can probably make a fair stab at an analogue PLL decoder given modern op amps. After all, Yamaha made an impressive one for the CT7000 using discrete transistors.

    Sadly, I note the comment that the old decoder ICs are now unavailable. The same seems to be the case for many old items like the stereo output filters that Toko used to sell.
  12. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Being someone who's mantra could be "death before digital", in as much as the design of equipment anyway, I would if necessary design a completely discrete decoder. As Jim says though, if going digital then you may as well go the whole hog. I believe such things are already available (I'll no doubt be informed of just how commonly available!) and recall seeing a review of IIRC a Sony all digital FM tuner which in spite of looking very cheap and plasticky was reckoned to be the best tuner they had ever heard by many of the people giving an opinion.

    As an aside here, it seems bizarre to me as an engineer of a certain age, that so called progress means we are now starting to have to do things (if, like me, an analogue or nothing guy) as we did in the '60's and early '70's once again due to most of the "high tech" that came out in the later 70's up to say 2000 becoming obsolete!
    I wonder if, in say 10 years time, it will no longer be possible to get output transistors which are optimised for non class D amplifiers? or audio op amps?

    It has already got to a state where many of our "go to" best parts as analogue designers are no longer available, or least only at a high price from companies specialising in selling hard to get or obsolete components (LM394, 2SK170, low noise discretes from Rohm such as 2SB737 to name a few that spring to mind... yes I know about the LSK170).

    I wouldn't be surprised if in 10-20 years time it was easy to make a 60's style valve amp but very difficult to make a 90's/noughties style SS amp!!
  13. davidsrsb

    davidsrsb pfm Member

    My experience is that these cheap SDR receivers work, but not very well. They don't handle weak signals among strong signals.
    What would be good solution would be a hybrid traditional 10.7MHz IF design, going digital after the limiter.
    Some of the modern "professional" RF amplifier and mixer ICs are really nice compared with the old dual gate mosfets.
    The old MC1310 and similar PLL stereo decoders worked beautifully with 1kHz tones, less well at 50Hz and 15kHz, which disturbed to crude PLL, which had far too wide pulling range and bandwidth
  14. Jim Audiomisc

    Jim Audiomisc pfm Member

    The very cheap SDRs are pretty poor in general. They may have no real RF filtering at all, and only 8-bit samples, albeit at high rate. Hence will tend to allow a high power signal to swamp a weaker one. However there are better SDRs about if you are prepared to look for them. FWIW I use a 'FUNCube Pro Plus' SDR (USB dongle) as an RF analyser [1]. *Much* cheaper than buying a good RF specan. It has a set of switchable RF filters, 24 bit sampling internally, etc. Lets me do RF measurements up to about 2 GHz.

    In this context, though, it has a limitation relevant to the thread. It runs at a sampling rate of 192k, which is too low for good Band II FM stereo reception. It does run 'I/Q' sampling so the actual usable RF reception bandwidth is a tad under 192k. Which would probably do OK for mono FM, although I've not tried that. But a bit too narrow for good stereo. However there are better SDRs if someone really wanted to go that route. But unlikely to be cheaper than a good old tuner. Might be fun as a project for someone whose mind leaned that way, though. 8-]

    All that said, yes, to me it would make more sense just to build an analogue decoder. Lacking the old high-performance chips, various designs could be done using op-amps or transistors. Question of how good you want to make it.

    [1] In my case mostly for higher frequencies, DVB-T/T2 in particular. Which, the way things are going, may cease before FM radio does!
  15. davidsrsb

    davidsrsb pfm Member

    I agree about the cheap SDRs. You could build a nice one with "professional" chips at a price, but for a hobbyist approach processing a filtered 10.7 MHz IF is much simpler to do.
    I have been wondering if DAB will vanish early, streaming over 5G could easily kill it. DAB has not even arrived in much of Asia yet
  16. Julf

    Julf Evil brother of Mark V Shaney

    I think the answer is a pretty clear "yes" - in countries with widespread unlimited 4G DAB is pretty dead already.
  17. davidsrsb

    davidsrsb pfm Member

    The UK has unusually stingy 4G data plans. I am on 40GB/month and can make that unlimited for music streaming for the equivalent of UKP1/month extra
  18. Jim Audiomisc

    Jim Audiomisc pfm Member

    I suspect that streaming is likely to kill off terrestrial TV broadcasting fairly soon. Wouldn't surprise me if DVB-T/T2 ceased before VHF FM or DAB radio. The way they are taking chunks of spectrum from TV for 4G, etc, indicates this. Which is problematic for some because, for those who lack money, a traditional TV set + license is cheaper than streaming HDTV over broadband or into a mobile.
  19. Paul R

    Paul R pfm Member

    I think terrestrial broadcasting is likely to outlive DBS. The public service broadcasters will be required to maintain it beyond any commercial justification.

  20. davidsrsb

    davidsrsb pfm Member

    Not really, the way that many DVB-T2 transmitters can use the same frequency for a multiplex as a SFN, compared with the old analog TV with repeaters on different channels to avoid interference, makes digital TV far more spectrum efficient. The entire UK could be covered with three multiplexes in about 100 MHz. Most of that is due to the transmitter antenna combiner needing gaps between its channels. This freed up the 700MHz to 800MHz and should ultimately release 600MHz to 700MHz, maybe even more

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